Manufacture of shaped articles from polymeric materials



Patented Aug. 6, 1940 MANUFACTURED! SHAPED ARTICLES FROM POLYMERICMATERIALS James Bache, Northwich,

Robertson Myles and- Leslie Longmore England, assignors to ImperialChemical Industries Limited, a corporation of Great Britain No Drawing.Application February "I, 1939, Se-

rial No. 255,166. In Great Britain February 11,

4 Claims.

This invention relates to the manufacture, from synthetic polymericmaterial, of films, tubes, threads and similar products.

The polymers used in the practice of this invention are the ethylenepolymers'obtained by the process described in application Serial Number123,722, filed February 2, 1937, by Fawcett, Gibson and Perrin, and inapplication Serial Number 157,810, filed August 6, 1937, by Perrin,Paton and Williams. The process described in the first mentionedapplication consists in subjecting ethylene to pressures in excess of500 atmospheres under controlled elevated temperature conditions. Thisprocedure results in various polymers of ethylene, the molecular weightof which varies depending particularly upon the pressure and temperatureconditions employed. By using pressures of more than 1000 atmos pheresand temperatures of the order of about 200 C., solid polymers ofethylene can be formed. Under these conditions the polymerizationreaction takes place smoothly, requiring several hours for completion.Or the more rapid reaction described in the second mentioned applicationmay be used. In this method a definite but small quantity of oxygenwhich may be as little as 0.01% but preferably 0.03% to 0.10% at 1500atmospheres, is included in the ethylene treated. The pressures are atleast 500 atmospheres and preferably at least 1000 atmospheres and below3000 atmospheres. The temperatures are between 100 C. and 400 C. andmore desirably from 150 C. to 250 C. Thus, as a specific instance ofobtaining the ethylene polymer, ethylene containing 0.05% oxygen iscompressed in a steel bomb to a total pressure of 1500 atmospheres andheated rapidly to 210 C. whereupon a very rapid change in pressurefollowed by a slow drop in pressure is observed. After five hoursheating at 210 C. the pressure is released and the product cooled. Underthese conditions an 80% yield of the solid polymer, based on theethylene used, is obtained. These solid ethylene polymers obtained asoutlined above melt or soften above about 100 C., usually between 110 C.and 200 C. depending upon the molecular weight of the particularpolymer, have a molecular weight in excess of 4000, and are essentiallysaturated products corresponding in composition substantially to (CH2)=.They are soluble in xylene at its boiling point and are unaifected byprolonged contact with air at ordinary temperature. These solid polymersas ordinarily prepared show a crystalline structure when subjected toX-ray diffraction analysis.

This invention has as an object an improved process for making films,tubes, threads, and the like from the ethylene polymers described above.A further object is the production of new and useful articles ofmanufacture. Other objects will appear hereinafter.

We have found that the ethylene polymers may be precipitated from theirsolutions in hot organic solvents and that this fact may be appliedunder certain conditions of operation to the economical manufacture ofarticles of the above mentioned kind. A hot concentrated solution of thepolymer in the form of a thin stream of the appropriate cross section isintroduced into a liquid miscible with the solvent which is a nonsolventfor the polymer.

-As a rule the temperature of precipitation should be above 70 C. andbelow 180 C. Below 70 C. the polymer tends to be precipitated as apowder and not in the desired coherent form. The best results areobtained at 80l00 C. The temperature of precipitation is mainlyconditioned by that of the bath of the precipitating liquid, but inpractice it is desirable that the solution of the polymer and the bath'both be at around the chosen precipitation temperature. Although thetemperature of precipitation may be above the melting point of thepolymer the material is so viscous that in practice it will retain theform which it is given during the precipitation. Both the solvent andthe precipitating liquid should be such that they do not boil at thedesired operating temperature. If necessary the operation may be carriedout under pressure in order to raise their boiling points.

As solvents may be used benzene and its homologues,tetrahydronaphthalene, decahydronaphthalene, trichlorethylene, highboiling petroleum ether, and, in general, any organic solvent which willgive a sufficiently concentrated solution of the polymer. As a rule theconcentration of polymer should not be less than about 20 per cent. Thehigher the concentration (upto the point at which the solution becomesunduly viscous), the more satisfactory appears to be the operation ofthe process. On the other handfif the concentration of polymer is belowabout 20 per cent; difficulty is experienced in obtaining satisfactoryproducts. The solvent is heated to obtain the necessary strength ofsolution, since the solubility of the polymer in the usual solvent isvery small.

The precipitating liquid should be highly miscible with the solvent ofthe polymer solution and have a low solubility for the polymer at thelow working temperature. Examples of suitable liquids include manyethers, alcohols, ketones and esters, e.- g. n-butyl ether, anisole,ethyl-isoamyl ether, n-propyl 'alcohol, n-butyl alcohol, cyclohexanol,ethylene glycol, secondary octyl alcohol, methyl amyl ketone,acetophenone, amyl acetate, methyl oleate, butyl phthalate and methylsuccinate. Mixtures of two or more of these liquids may be used.

In the production of threads or fibers, the polymer solution may beextruded through a suitable orifice of the type of a spinneret,projecting below the surface of the precipitant liquid. The extruded orcoagulated thread is drawn off at a suitable speed to give the desiredthickness, and at the same time this process may be employed to apply -adrawing efiect whereby the molecules of the polymer are orientatedparallel to the direction of the drawing, thus giving added strength andluster to the thread. The thickness may also be regulated by thestrength of the polymer solution.

Any residual solvent adhering to the extruded material may be removedsimply by a suitably arranged hot air blast or application of partialvacuum. In cases where precipitants of low volatility (such asdibutylphthalate) are employed, it is advantageous first to pass thematerial through a bath of low boiling solvent such as ethyl ether orpetroleum ether.

If desired the single threads may be gathered into bundles or hankswhich can be cut to form staple fibers of any desired length, e. g. 2inches. The drawing out of the threads may be partly accomplished asdescribed above, and by stretching in bulk a hank of threads the threadsmay be fully cold drawn prior to cutting into staple fibers. Duringstretching the molecules become more and more orientated in thedirection of pull, and finally complete orientation is obtained when thethread has been extended to about five times its original length.Slivers of the staple fiber may be converted by twisting and pullingoperations which are well known in the art of manufacturing textilesinto yarn or twist from which fabrics may be woven.

In carrying out the invention we prefer to use polymers of molecularweight of at least 4000, and preferably 6000 or over. The mechanicalstrength of the products increases with the molecular weight of thepolymer employed.

In general the strength of the products may be increased by subjectinthem to treatment adapted to produce partial or complete orientation ofthe molecules in a given direction. In the case of threads or tubes thismay be accomplished by drawing as explained above; in the case of films,sheets or ribbons the strengthening treatment may consist in coldrolling, i. e., rolling at a temperature substantially below thesoftening temperature of the polymer. The maximum increase of strengthis obtained when the thickness of the material is reduced to aboutone-fifth of its original value. If desired. the films, sheets orribbons produced according to the invention may be polished bysubiecting them to slight pressure between two heated highly polishedsurfaces.

The following examples are illustrative of the methods used inpracticing our invention:

Example I In this example is described the production of a singlecontinuous thread of ethylene polymer. A 40 per cent solution in xyleneof a polymer of molecular weight about 15,000, maintained at atemperature of 96 C., is extruded under a pressure of about 24" of waterthrough a jet 0.5 mm. diameter into a bath of n-butyl alcohol or amixture of n-amyl alcohol and butyl phthalate at the same temperature.By means of a reel, the resulting viscous thread is drawn off throughthe bath and into a warm atmosphere, the speed of drawing beingregulated to give a final diameter of 0.015 mm. A length of passagethrough the bath of 1 may conveniently be allowed.

The residual solvent and the precipitating liquid adhering to thethreadare then removed by washing ina bath of petroleum ether, followed bydrying in a current of warm air. The continuous thread so obtained maybe increased in strength and reduced in diameter by stretching in thecold.

Example I! In this example is described the production of a thin film ofethylene polymer. A solution is prepared as in Example I and ismaintained at a temperature of 95 C. The solution is then introduced,suitably by means of a narrow slit, in an even film across the face of aheated revolving drum. The drum dips in a bath of n-propyl alcoholmaintained at a temperature of 90 C. As the film of solution passesthrough the bath, the xylene is taken up by the n-propyl alcohol and afilm of polymer is precipitated on the surface of the drum. The film isdetached from the drum as it rises out of the bath and is collected upona reel.

The molecular weights mentioned herein were obtained by the method fordetermining the molecular weights of polymers of high molecular weightdevised by H. Staudinger (see Berichte der deutschen chemischen Ges.1934, 67B, 1247 et seq.) this method being based upon the measurement ofthe viscosity of a solution of the polymer in a solvent(tetrahydronaphthalene). As this method may not be susceptible of a highdegree of accuracy, the values given in this specification should be inall cases regarded as approximate.

The melting or softening points of the polymers were measured by a belland ring method in which a film of polymer, supported over a ring, isheated by immersion in a heated nonsolvent and a small steel ball isplaced over the film. The melting or softening point is taken to be thetemperature at which the polymer is so sufficiently soft that the ballpasses through the ring. In this connection it is to be noted that thepolymer does not melt sharply but changes slowly from a solid to a moreor less viscous liquid.

The present method provides a convenient method adapted to the largescale production of films. tubes. threads and similar articles. Thepresent invention is particularly adapted to the production of finerthreads, films, and tapes than has heretofore been possible.

The products obtained accordling to the invention are highly resistantto water and many chemicals. The threads are characterized by strength,elasticity, cohesion and lightness. The films, sheets and ribbons may beused for wrapping and protective purposes in general. The products alsohave excellent dielectric properties and may be used for electricalinsulation.

As many' apparently widely different embodiments of this invention maybe made without departing from the spirit and scope thereof, it is to beunderstood that we do not limit ourselves to the specific embodimentsthereof except as defined in the appended claims.

We claim:

1. A method for making films, tubes, threads. tapes and the like whichcomprises introducing a stream of a hot solution of a normally solidethylene polymer into a precipitating liquid which is miscible with thesolvent of said solution and which is a non-solvent for the polymer,said solution and precipitating bath being at a temperature of at leastC.

2. A method for making films, tubes, threads, tapes, and the like whichcomprises introducing a stream of a heated solution of a normally solidethylene polymer in an organic solvent, said solution containing notless than about 20% of the ethylene polymer, into a heated liquid atelevated temperature, which liquid is miscible with said solvent andwhich is a substantially non-solvent for the polymer, the temperature ofprecipitation of the polymer by said liquid being at a temperature offrom 70 C. to C.

3. A method of manufacturing threads, films, tubes, tapes, and the likewhich comprises extruding a solution of a normally solid polymer ofethylene having a molecular weight above 4000 into a liquid which ismiscible with the solvent used but is a non-solvent for the ethylenepolymer, the extrusion being through an orifice of larger cross sectionthan the product required, the product being drawn out of the liquid ata higher rate than the rate of extrusion whereby the desired size ofcross section is obtained, said solution and liquid being at atemperature of at least 70 C.

4. A method of manufacturing staple fibre which comprises extruding asolution of a normally solid polymerof ethylene having a molecularweight above 4000 into a liquid which is miscible with the solvent butis itself a nonsolvent for the ethylene polymer, drying the thread soformed, and subjecting it to a tensioning process in the cold wherebythe molecules are oriented along the length of the thread, said solutionand liquid being at a temperature of at least '70 C.

JAMES ROBERTSON MYLES. LESLIE L. BACHE.

